Quirky website may crack flu riddle

Scientists hope a popular US website that tracks the geographical circulation of money could offer new clues into how infectious diseases like bird flu spread.

Money, like diseases, is carried by people around the world, so what better way to plot the spread of a potential influenza pandemic than to track the circulation of dollar bills, researchers reason.

Researchers in Germany and the United States did just that to develop a mathematical model of human travel that can be used to plot the spread of future pandemics.

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"There are some universal rules governing human travel and they can be used to develop a new class of model for the spread of infectious disease," said Dr Dirk Brockmann, a physicist at the Max Planck Institute for Dynamics and Self-Organisation in Gottingen, Germany.

Health experts fear the H5N1 bird flu virus that has killed at least 82 people in six countries since 2003 could mutate into a highly infectious strain in humans that could cause the next pandemic.

"We can now plug in the parameter ranges that we think will apply to influenza and then simulate a pandemic that runs through Europe and see what happens," said Brockmann, who reported the findings today in the journal Nature.

In addition to giving insights into how an infectious disease would spread, mathematical models and computer simulations could help to develop measures to take against it, he added.

Human movement is a main cause of the spread of infectious disease but with modern day travel involving boats, planes, trains, cars and other means of transport it is virtually impossible to compile a comprehensive set of data on travel.

The scientists analysed information from http://www.wheresgeorge.com, an online bill tracking internet site. Users, most of whom mark their bills with the website address, register on the site and follow the trail of their money after they spend it.

About 50 million banknotes have been registered on the site, according to Brockmann.

The information from the site enabled the researchers to develop a mathematical theory of human travel behaviour. When they compared their results with traffic flow of aviation networks in the United States, they found it correlated very closely.

"This is a very good estimate of how humans travel," Brockmann said.

"The things that we observed in the United States may also be valid for Europe or Canada. If that is so, we can develop models for the spread of infectious disease that can reveal universal characteristics of modern pandemics," he added.